The very most critical part of a roof installation is to follow the manufacturer’s specifications. The are printed on the inside of the bundle of every shingle. This will determine if the manufacturer will stand behind their warranty which is typically 25 or 30 years. Recently the warranty has been extended to Lifetime, however if the nails are not properly spaced horizontally and vertically or the shingles are started in a way that is not according to the manufacturer’s specifications, you will have no warranty and the roof may not look as great as it was designed.